pc-bios/s390-ccw: add vdev object to store all device details

Add VDev "object" as a container for all device-related items.
The default object is static.

Leverage dependency on many different device-related globals.
Make them syntactically visible.

Signed-off-by: Eugene (jno) Dvurechenski <jno@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>